drivers/watchdog/watchdog_dev.c

   1 // SPDX-License-Identifier: GPL-2.0+
   2 /*
   3  *      watchdog_dev.c
   4  *
   5  *      (c) Copyright 2008-2011 Alan Cox <alan@lxorguk.ukuu.org.uk>,
   6  *                                              All Rights Reserved.
   7  *
   8  *      (c) Copyright 2008-2011 Wim Van Sebroeck <wim@iguana.be>.
   9  *
  10  *      (c) Copyright 2021 Hewlett Packard Enterprise Development LP.
  11  *
  12  *      This source code is part of the generic code that can be used
  13  *      by all the watchdog timer drivers.
  14  *
  15  *      This part of the generic code takes care of the following
  16  *      misc device: /dev/watchdog.
  17  *
  18  *      Based on source code of the following authors:
  19  *        Matt Domsch <Matt_Domsch@dell.com>,
  20  *        Rob Radez <rob@osinvestor.com>,
  21  *        Rusty Lynch <rusty@linux.co.intel.com>
  22  *        Satyam Sharma <satyam@infradead.org>
  23  *        Randy Dunlap <randy.dunlap@oracle.com>
  24  *
  25  *      Neither Alan Cox, CymruNet Ltd., Wim Van Sebroeck nor Iguana vzw.
  26  *      admit liability nor provide warranty for any of this software.
  27  *      This material is provided "AS-IS" and at no charge.
  28  */
  29
  30 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  31
  32 #include <linux/cdev.h>         /* For character device */
  33 #include <linux/errno.h>        /* For the -ENODEV/... values */
  34 #include <linux/fs.h>           /* For file operations */
  35 #include <linux/init.h>         /* For __init/__exit/... */
  36 #include <linux/hrtimer.h>      /* For hrtimers */
  37 #include <linux/kernel.h>       /* For printk/panic/... */
  38 #include <linux/kstrtox.h>      /* For kstrto* */
  39 #include <linux/kthread.h>      /* For kthread_work */
  40 #include <linux/miscdevice.h>   /* For handling misc devices */
  41 #include <linux/module.h>       /* For module stuff/... */
  42 #include <linux/mutex.h>        /* For mutexes */
  43 #include <linux/slab.h>         /* For memory functions */
  44 #include <linux/types.h>        /* For standard types (like size_t) */
  45 #include <linux/watchdog.h>     /* For watchdog specific items */
  46 #include <linux/uaccess.h>      /* For copy_to_user/put_user/... */
  47
  48 #include "watchdog_core.h"
  49 #include "watchdog_pretimeout.h"
  50
  51 #include <trace/events/watchdog.h>
  52
  53 /* the dev_t structure to store the dynamically allocated watchdog devices */
  54 static dev_t watchdog_devt;
  55 /* Reference to watchdog device behind /dev/watchdog */
  56 static struct watchdog_core_data *old_wd_data;
  57
  58 static struct kthread_worker *watchdog_kworker;
  59
  60 static bool handle_boot_enabled =
  61         IS_ENABLED(CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED);
  62
  63 static unsigned open_timeout = CONFIG_WATCHDOG_OPEN_TIMEOUT;
  64
  65 static bool watchdog_past_open_deadline(struct watchdog_core_data *data)
  66 {
  67         return ktime_after(ktime_get(), data->open_deadline);
  68 }
  69
  70 static void watchdog_set_open_deadline(struct watchdog_core_data *data)
  71 {
  72         data->open_deadline = open_timeout ?
  73                 ktime_get() + ktime_set(open_timeout, 0) : KTIME_MAX;
  74 }
  75
  76 static inline bool watchdog_need_worker(struct watchdog_device *wdd)
  77 {
  78         /* All variables in milli-seconds */
  79         unsigned int hm = wdd->max_hw_heartbeat_ms;
  80         unsigned int t = wdd->timeout * 1000;
  81
  82         /*
  83          * A worker to generate heartbeat requests is needed if all of the
  84          * following conditions are true.
  85          * - Userspace activated the watchdog.
  86          * - The driver provided a value for the maximum hardware timeout, and
  87          *   thus is aware that the framework supports generating heartbeat
  88          *   requests.
  89          * - Userspace requests a longer timeout than the hardware can handle.
  90          *
  91          * Alternatively, if userspace has not opened the watchdog
  92          * device, we take care of feeding the watchdog if it is
  93          * running.
  94          */
  95         return (hm && watchdog_active(wdd) && t > hm) ||
  96                 (t && !watchdog_active(wdd) && watchdog_hw_running(wdd));
  97 }
  98
  99 static ktime_t watchdog_next_keepalive(struct watchdog_device *wdd)
 100 {
 101         struct watchdog_core_data *wd_data = wdd->wd_data;
 102         unsigned int timeout_ms = wdd->timeout * 1000;
 103         ktime_t keepalive_interval;
 104         ktime_t last_heartbeat, latest_heartbeat;
 105         ktime_t virt_timeout;
 106         unsigned int hw_heartbeat_ms;
 107
 108         if (watchdog_active(wdd))
 109                 virt_timeout = ktime_add(wd_data->last_keepalive,
 110                                          ms_to_ktime(timeout_ms));
 111         else
 112                 virt_timeout = wd_data->open_deadline;
 113
 114         hw_heartbeat_ms = min_not_zero(timeout_ms, wdd->max_hw_heartbeat_ms);
 115         keepalive_interval = ms_to_ktime(hw_heartbeat_ms / 2);
 116
 117         /*
 118          * To ensure that the watchdog times out wdd->timeout seconds
 119          * after the most recent ping from userspace, the last
 120          * worker ping has to come in hw_heartbeat_ms before this timeout.
 121          */
 122         last_heartbeat = ktime_sub(virt_timeout, ms_to_ktime(hw_heartbeat_ms));
 123         latest_heartbeat = ktime_sub(last_heartbeat, ktime_get());
 124         if (ktime_before(latest_heartbeat, keepalive_interval))
 125                 return latest_heartbeat;
 126         return keepalive_interval;
 127 }
 128
 129 static inline void watchdog_update_worker(struct watchdog_device *wdd)
 130 {
 131         struct watchdog_core_data *wd_data = wdd->wd_data;
 132
 133         if (watchdog_need_worker(wdd)) {
 134                 ktime_t t = watchdog_next_keepalive(wdd);
 135
 136                 if (t > 0)
 137                         hrtimer_start(&wd_data->timer, t,
 138                                       HRTIMER_MODE_REL_HARD);
 139         } else {
 140                 hrtimer_cancel(&wd_data->timer);
 141         }
 142 }
 143
 144 static int __watchdog_ping(struct watchdog_device *wdd)
 145 {
 146         struct watchdog_core_data *wd_data = wdd->wd_data;
 147         ktime_t earliest_keepalive, now;
 148         int err;
 149
 150         earliest_keepalive = ktime_add(wd_data->last_hw_keepalive,
 151                                        ms_to_ktime(wdd->min_hw_heartbeat_ms));
 152         now = ktime_get();
 153
 154         if (ktime_after(earliest_keepalive, now)) {
 155                 hrtimer_start(&wd_data->timer,
 156                               ktime_sub(earliest_keepalive, now),
 157                               HRTIMER_MODE_REL_HARD);
 158                 return 0;
 159         }
 160
 161         wd_data->last_hw_keepalive = now;
 162
 163         if (wdd->ops->ping) {
 164                 err = wdd->ops->ping(wdd);  /* ping the watchdog */
 165                 trace_watchdog_ping(wdd, err);
 166         } else {
 167                 err = wdd->ops->start(wdd); /* restart watchdog */
 168                 trace_watchdog_start(wdd, err);
 169         }
 170
 171         if (err == 0)
 172                 watchdog_hrtimer_pretimeout_start(wdd);
 173
 174         watchdog_update_worker(wdd);
 175
 176         return err;
 177 }
 178
 179 /*
 180  * watchdog_ping - ping the watchdog
 181  * @wdd: The watchdog device to ping
 182  *
 183  * If the watchdog has no own ping operation then it needs to be
 184  * restarted via the start operation. This wrapper function does
 185  * exactly that.
 186  * We only ping when the watchdog device is running.
 187  * The caller must hold wd_data->lock.
 188  *
 189  * Return: 0 on success, error otherwise.
 190  */
 191 static int watchdog_ping(struct watchdog_device *wdd)
 192 {
 193         struct watchdog_core_data *wd_data = wdd->wd_data;
 194
 195         if (!watchdog_hw_running(wdd))
 196                 return 0;
 197
 198         set_bit(_WDOG_KEEPALIVE, &wd_data->status);
 199
 200         wd_data->last_keepalive = ktime_get();
 201         return __watchdog_ping(wdd);
 202 }
 203
 204 static bool watchdog_worker_should_ping(struct watchdog_core_data *wd_data)
 205 {
 206         struct watchdog_device *wdd = wd_data->wdd;
 207
 208         if (!wdd)
 209                 return false;
 210
 211         if (watchdog_active(wdd))
 212                 return true;
 213
 214         return watchdog_hw_running(wdd) && !watchdog_past_open_deadline(wd_data);
 215 }
 216
 217 static void watchdog_ping_work(struct kthread_work *work)
 218 {
 219         struct watchdog_core_data *wd_data;
 220
 221         wd_data = container_of(work, struct watchdog_core_data, work);
 222
 223         mutex_lock(&wd_data->lock);
 224         if (watchdog_worker_should_ping(wd_data))
 225                 __watchdog_ping(wd_data->wdd);
 226         mutex_unlock(&wd_data->lock);
 227 }
 228
 229 static enum hrtimer_restart watchdog_timer_expired(struct hrtimer *timer)
 230 {
 231         struct watchdog_core_data *wd_data;
 232
 233         wd_data = container_of(timer, struct watchdog_core_data, timer);
 234
 235         kthread_queue_work(watchdog_kworker, &wd_data->work);
 236         return HRTIMER_NORESTART;
 237 }
 238
 239 /*
 240  * watchdog_start - wrapper to start the watchdog
 241  * @wdd: The watchdog device to start
 242  *
 243  * Start the watchdog if it is not active and mark it active.
 244  * The caller must hold wd_data->lock.
 245  *
 246  * Return: 0 on success or a negative errno code for failure.
 247  */
 248 static int watchdog_start(struct watchdog_device *wdd)
 249 {
 250         struct watchdog_core_data *wd_data = wdd->wd_data;
 251         ktime_t started_at;
 252         int err;
 253
 254         if (watchdog_active(wdd))
 255                 return 0;
 256
 257         set_bit(_WDOG_KEEPALIVE, &wd_data->status);
 258
 259         started_at = ktime_get();
 260         if (watchdog_hw_running(wdd) && wdd->ops->ping) {
 261                 err = __watchdog_ping(wdd);
 262                 if (err == 0) {
 263                         set_bit(WDOG_ACTIVE, &wdd->status);
 264                         watchdog_hrtimer_pretimeout_start(wdd);
 265                 }
 266         } else {
 267                 err = wdd->ops->start(wdd);
 268                 trace_watchdog_start(wdd, err);
 269                 if (err == 0) {
 270                         set_bit(WDOG_ACTIVE, &wdd->status);
 271                         set_bit(WDOG_HW_RUNNING, &wdd->status);
 272                         wd_data->last_keepalive = started_at;
 273                         wd_data->last_hw_keepalive = started_at;
 274                         watchdog_update_worker(wdd);
 275                         watchdog_hrtimer_pretimeout_start(wdd);
 276                 }
 277         }
 278
 279         return err;
 280 }
 281
 282 /*
 283  * watchdog_stop - wrapper to stop the watchdog
 284  * @wdd: The watchdog device to stop
 285  *
 286  * Stop the watchdog if it is still active and unmark it active.
 287  * If the 'nowayout' feature was set, the watchdog cannot be stopped.
 288  * The caller must hold wd_data->lock.
 289  *
 290  * Return: 0 on success or a negative errno code for failure.
 291  */
 292 static int watchdog_stop(struct watchdog_device *wdd)
 293 {
 294         int err = 0;
 295
 296         if (!watchdog_active(wdd))
 297                 return 0;
 298
 299         if (test_bit(WDOG_NO_WAY_OUT, &wdd->status)) {
 300                 pr_info("watchdog%d: nowayout prevents watchdog being stopped!\n",
 301                         wdd->id);
 302                 return -EBUSY;
 303         }
 304
 305         if (wdd->ops->stop) {
 306                 clear_bit(WDOG_HW_RUNNING, &wdd->status);
 307                 err = wdd->ops->stop(wdd);
 308                 trace_watchdog_stop(wdd, err);
 309         } else {
 310                 set_bit(WDOG_HW_RUNNING, &wdd->status);
 311         }
 312
 313         if (err == 0) {
 314                 clear_bit(WDOG_ACTIVE, &wdd->status);
 315                 watchdog_update_worker(wdd);
 316                 watchdog_hrtimer_pretimeout_stop(wdd);
 317         }
 318
 319         return err;
 320 }
 321
 322 /*
 323  * watchdog_get_status - wrapper to get the watchdog status
 324  * @wdd: The watchdog device to get the status from
 325  *
 326  * Get the watchdog's status flags.
 327  * The caller must hold wd_data->lock.
 328  *
 329  * Return: watchdog's status flags.
 330  */
 331 static unsigned int watchdog_get_status(struct watchdog_device *wdd)
 332 {
 333         struct watchdog_core_data *wd_data = wdd->wd_data;
 334         unsigned int status;
 335
 336         if (wdd->ops->status)
 337                 status = wdd->ops->status(wdd);
 338         else
 339                 status = wdd->bootstatus & (WDIOF_CARDRESET |
 340                                             WDIOF_OVERHEAT |
 341                                             WDIOF_FANFAULT |
 342                                             WDIOF_EXTERN1 |
 343                                             WDIOF_EXTERN2 |
 344                                             WDIOF_POWERUNDER |
 345                                             WDIOF_POWEROVER);
 346
 347         if (test_bit(_WDOG_ALLOW_RELEASE, &wd_data->status))
 348                 status |= WDIOF_MAGICCLOSE;
 349
 350         if (test_and_clear_bit(_WDOG_KEEPALIVE, &wd_data->status))
 351                 status |= WDIOF_KEEPALIVEPING;
 352
 353         if (IS_ENABLED(CONFIG_WATCHDOG_HRTIMER_PRETIMEOUT))
 354                 status |= WDIOF_PRETIMEOUT;
 355
 356         return status;
 357 }
 358
 359 /*
 360  * watchdog_set_timeout - set the watchdog timer timeout
 361  * @wdd:        The watchdog device to set the timeout for
 362  * @timeout:    Timeout to set in seconds
 363  *
 364  * The caller must hold wd_data->lock.
 365  *
 366  * Return: 0 if successful, error otherwise.
 367  */
 368 static int watchdog_set_timeout(struct watchdog_device *wdd,
 369                                                         unsigned int timeout)
 370 {
 371         int err = 0;
 372
 373         if (!(wdd->info->options & WDIOF_SETTIMEOUT))
 374                 return -EOPNOTSUPP;
 375
 376         if (watchdog_timeout_invalid(wdd, timeout))
 377                 return -EINVAL;
 378
 379         if (wdd->ops->set_timeout) {
 380                 err = wdd->ops->set_timeout(wdd, timeout);
 381                 trace_watchdog_set_timeout(wdd, timeout, err);
 382         } else {
 383                 wdd->timeout = timeout;
 384                 /* Disable pretimeout if it doesn't fit the new timeout */
 385                 if (wdd->pretimeout >= wdd->timeout)
 386                         wdd->pretimeout = 0;
 387         }
 388
 389         watchdog_update_worker(wdd);
 390
 391         return err;
 392 }
 393
 394 /*
 395  * watchdog_set_pretimeout - set the watchdog timer pretimeout
 396  * @wdd:        The watchdog device to set the timeout for
 397  * @timeout:    pretimeout to set in seconds
 398  *
 399  * Return: 0 if successful, error otherwise.
 400  */
 401 static int watchdog_set_pretimeout(struct watchdog_device *wdd,
 402                                    unsigned int timeout)
 403 {
 404         int err = 0;
 405
 406         if (!watchdog_have_pretimeout(wdd))
 407                 return -EOPNOTSUPP;
 408
 409         if (watchdog_pretimeout_invalid(wdd, timeout))
 410                 return -EINVAL;
 411
 412         if (wdd->ops->set_pretimeout && (wdd->info->options & WDIOF_PRETIMEOUT))
 413                 err = wdd->ops->set_pretimeout(wdd, timeout);
 414         else
 415                 wdd->pretimeout = timeout;
 416
 417         return err;
 418 }
 419
 420 /*
 421  * watchdog_get_timeleft - wrapper to get the time left before a reboot
 422  * @wdd:        The watchdog device to get the remaining time from
 423  * @timeleft:   The time that's left
 424  *
 425  * Get the time before a watchdog will reboot (if not pinged).
 426  * The caller must hold wd_data->lock.
 427  *
 428  * Return: 0 if successful, error otherwise.
 429  */
 430 static int watchdog_get_timeleft(struct watchdog_device *wdd,
 431                                                         unsigned int *timeleft)
 432 {
 433         *timeleft = 0;
 434
 435         if (!wdd->ops->get_timeleft)
 436                 return -EOPNOTSUPP;
 437
 438         *timeleft = wdd->ops->get_timeleft(wdd);
 439
 440         return 0;
 441 }
 442
 443 #ifdef CONFIG_WATCHDOG_SYSFS
 444 static ssize_t nowayout_show(struct device *dev, struct device_attribute *attr,
 445                                 char *buf)
 446 {
 447         struct watchdog_device *wdd = dev_get_drvdata(dev);
 448
 449         return sysfs_emit(buf, "%d\n", !!test_bit(WDOG_NO_WAY_OUT,
 450                                                   &wdd->status));
 451 }
 452
 453 static ssize_t nowayout_store(struct device *dev, struct device_attribute *attr,
 454                                 const char *buf, size_t len)
 455 {
 456         struct watchdog_device *wdd = dev_get_drvdata(dev);
 457         unsigned int value;
 458         int ret;
 459
 460         ret = kstrtouint(buf, 0, &value);
 461         if (ret)
 462                 return ret;
 463         if (value > 1)
 464                 return -EINVAL;
 465         /* nowayout cannot be disabled once set */
 466         if (test_bit(WDOG_NO_WAY_OUT, &wdd->status) && !value)
 467                 return -EPERM;
 468         watchdog_set_nowayout(wdd, value);
 469         return len;
 470 }
 471 static DEVICE_ATTR_RW(nowayout);
 472
 473 static ssize_t status_show(struct device *dev, struct device_attribute *attr,
 474                                 char *buf)
 475 {
 476         struct watchdog_device *wdd = dev_get_drvdata(dev);
 477         struct watchdog_core_data *wd_data = wdd->wd_data;
 478         unsigned int status;
 479
 480         mutex_lock(&wd_data->lock);
 481         status = watchdog_get_status(wdd);
 482         mutex_unlock(&wd_data->lock);
 483
 484         return sysfs_emit(buf, "0x%x\n", status);
 485 }
 486 static DEVICE_ATTR_RO(status);
 487
 488 static ssize_t bootstatus_show(struct device *dev,
 489                                 struct device_attribute *attr, char *buf)
 490 {
 491         struct watchdog_device *wdd = dev_get_drvdata(dev);
 492
 493         return sysfs_emit(buf, "%u\n", wdd->bootstatus);
 494 }
 495 static DEVICE_ATTR_RO(bootstatus);
 496
 497 static ssize_t timeleft_show(struct device *dev, struct device_attribute *attr,
 498                                 char *buf)
 499 {
 500         struct watchdog_device *wdd = dev_get_drvdata(dev);
 501         struct watchdog_core_data *wd_data = wdd->wd_data;
 502         ssize_t status;
 503         unsigned int val;
 504
 505         mutex_lock(&wd_data->lock);
 506         status = watchdog_get_timeleft(wdd, &val);
 507         mutex_unlock(&wd_data->lock);
 508         if (!status)
 509                 status = sysfs_emit(buf, "%u\n", val);
 510
 511         return status;
 512 }
 513 static DEVICE_ATTR_RO(timeleft);
 514
 515 static ssize_t timeout_show(struct device *dev, struct device_attribute *attr,
 516                                 char *buf)
 517 {
 518         struct watchdog_device *wdd = dev_get_drvdata(dev);
 519
 520         return sysfs_emit(buf, "%u\n", wdd->timeout);
 521 }
 522 static DEVICE_ATTR_RO(timeout);
 523
 524 static ssize_t min_timeout_show(struct device *dev,
 525                                 struct device_attribute *attr, char *buf)
 526 {
 527         struct watchdog_device *wdd = dev_get_drvdata(dev);
 528
 529         return sysfs_emit(buf, "%u\n", wdd->min_timeout);
 530 }
 531 static DEVICE_ATTR_RO(min_timeout);
 532
 533 static ssize_t max_timeout_show(struct device *dev,
 534                                 struct device_attribute *attr, char *buf)
 535 {
 536         struct watchdog_device *wdd = dev_get_drvdata(dev);
 537
 538         return sysfs_emit(buf, "%u\n", wdd->max_timeout);
 539 }
 540 static DEVICE_ATTR_RO(max_timeout);
 541
 542 static ssize_t pretimeout_show(struct device *dev,
 543                                struct device_attribute *attr, char *buf)
 544 {
 545         struct watchdog_device *wdd = dev_get_drvdata(dev);
 546
 547         return sysfs_emit(buf, "%u\n", wdd->pretimeout);
 548 }
 549 static DEVICE_ATTR_RO(pretimeout);
 550
 551 static ssize_t options_show(struct device *dev, struct device_attribute *attr,
 552                             char *buf)
 553 {
 554         struct watchdog_device *wdd = dev_get_drvdata(dev);
 555
 556         return sysfs_emit(buf, "0x%x\n", wdd->info->options);
 557 }
 558 static DEVICE_ATTR_RO(options);
 559
 560 static ssize_t fw_version_show(struct device *dev, struct device_attribute *attr,
 561                                char *buf)
 562 {
 563         struct watchdog_device *wdd = dev_get_drvdata(dev);
 564
 565         return sysfs_emit(buf, "%d\n", wdd->info->firmware_version);
 566 }
 567 static DEVICE_ATTR_RO(fw_version);
 568
 569 static ssize_t identity_show(struct device *dev, struct device_attribute *attr,
 570                                 char *buf)
 571 {
 572         struct watchdog_device *wdd = dev_get_drvdata(dev);
 573
 574         return sysfs_emit(buf, "%s\n", wdd->info->identity);
 575 }
 576 static DEVICE_ATTR_RO(identity);
 577
 578 static ssize_t state_show(struct device *dev, struct device_attribute *attr,
 579                                 char *buf)
 580 {
 581         struct watchdog_device *wdd = dev_get_drvdata(dev);
 582
 583         if (watchdog_active(wdd))
 584                 return sysfs_emit(buf, "active\n");
 585
 586         return sysfs_emit(buf, "inactive\n");
 587 }
 588 static DEVICE_ATTR_RO(state);
 589
 590 static ssize_t pretimeout_available_governors_show(struct device *dev,
 591                                    struct device_attribute *attr, char *buf)
 592 {
 593         return watchdog_pretimeout_available_governors_get(buf);
 594 }
 595 static DEVICE_ATTR_RO(pretimeout_available_governors);
 596
 597 static ssize_t pretimeout_governor_show(struct device *dev,
 598                                         struct device_attribute *attr,
 599                                         char *buf)
 600 {
 601         struct watchdog_device *wdd = dev_get_drvdata(dev);
 602
 603         return watchdog_pretimeout_governor_get(wdd, buf);
 604 }
 605
 606 static ssize_t pretimeout_governor_store(struct device *dev,
 607                                          struct device_attribute *attr,
 608                                          const char *buf, size_t count)
 609 {
 610         struct watchdog_device *wdd = dev_get_drvdata(dev);
 611         int ret = watchdog_pretimeout_governor_set(wdd, buf);
 612
 613         if (!ret)
 614                 ret = count;
 615
 616         return ret;
 617 }
 618 static DEVICE_ATTR_RW(pretimeout_governor);
 619
 620 static umode_t wdt_is_visible(struct kobject *kobj, struct attribute *attr,
 621                                 int n)
 622 {
 623         struct device *dev = kobj_to_dev(kobj);
 624         struct watchdog_device *wdd = dev_get_drvdata(dev);
 625         umode_t mode = attr->mode;
 626
 627         if (attr == &dev_attr_timeleft.attr && !wdd->ops->get_timeleft)
 628                 mode = 0;
 629         else if (attr == &dev_attr_pretimeout.attr && !watchdog_have_pretimeout(wdd))
 630                 mode = 0;
 631         else if ((attr == &dev_attr_pretimeout_governor.attr ||
 632                   attr == &dev_attr_pretimeout_available_governors.attr) &&
 633                  (!watchdog_have_pretimeout(wdd) || !IS_ENABLED(CONFIG_WATCHDOG_PRETIMEOUT_GOV)))
 634                 mode = 0;
 635
 636         return mode;
 637 }
 638 static struct attribute *wdt_attrs[] = {
 639         &dev_attr_state.attr,
 640         &dev_attr_options.attr,
 641         &dev_attr_fw_version.attr,
 642         &dev_attr_identity.attr,
 643         &dev_attr_timeout.attr,
 644         &dev_attr_min_timeout.attr,
 645         &dev_attr_max_timeout.attr,
 646         &dev_attr_pretimeout.attr,
 647         &dev_attr_timeleft.attr,
 648         &dev_attr_bootstatus.attr,
 649         &dev_attr_status.attr,
 650         &dev_attr_nowayout.attr,
 651         &dev_attr_pretimeout_governor.attr,
 652         &dev_attr_pretimeout_available_governors.attr,
 653         NULL,
 654 };
 655
 656 static const struct attribute_group wdt_group = {
 657         .attrs = wdt_attrs,
 658         .is_visible = wdt_is_visible,
 659 };
 660 __ATTRIBUTE_GROUPS(wdt);
 661 #else
 662 #define wdt_groups      NULL
 663 #endif
 664
 665 /*
 666  * watchdog_ioctl_op - call the watchdog drivers ioctl op if defined
 667  * @wdd: The watchdog device to do the ioctl on
 668  * @cmd: Watchdog command
 669  * @arg: Argument pointer
 670  *
 671  * The caller must hold wd_data->lock.
 672  *
 673  * Return: 0 if successful, error otherwise.
 674  */
 675 static int watchdog_ioctl_op(struct watchdog_device *wdd, unsigned int cmd,
 676                                                         unsigned long arg)
 677 {
 678         if (!wdd->ops->ioctl)
 679                 return -ENOIOCTLCMD;
 680
 681         return wdd->ops->ioctl(wdd, cmd, arg);
 682 }
 683
 684 /*
 685  * watchdog_write - writes to the watchdog
 686  * @file:       File from VFS
 687  * @data:       User address of data
 688  * @len:        Length of data
 689  * @ppos:       Pointer to the file offset
 690  *
 691  * A write to a watchdog device is defined as a keepalive ping.
 692  * Writing the magic 'V' sequence allows the next close to turn
 693  * off the watchdog (if 'nowayout' is not set).
 694  *
 695  * Return: @len if successful, error otherwise.
 696  */
 697 static ssize_t watchdog_write(struct file *file, const char __user *data,
 698                                                 size_t len, loff_t *ppos)
 699 {
 700         struct watchdog_core_data *wd_data = file->private_data;
 701         struct watchdog_device *wdd;
 702         int err;
 703         size_t i;
 704         char c;
 705
 706         if (len == 0)
 707                 return 0;
 708
 709         /*
 710          * Note: just in case someone wrote the magic character
 711          * five months ago...
 712          */
 713         clear_bit(_WDOG_ALLOW_RELEASE, &wd_data->status);
 714
 715         /* scan to see whether or not we got the magic character */
 716         for (i = 0; i != len; i++) {
 717                 if (get_user(c, data + i))
 718                         return -EFAULT;
 719                 if (c == 'V')
 720                         set_bit(_WDOG_ALLOW_RELEASE, &wd_data->status);
 721         }
 722
 723         /* someone wrote to us, so we send the watchdog a keepalive ping */
 724
 725         err = -ENODEV;
 726         mutex_lock(&wd_data->lock);
 727         wdd = wd_data->wdd;
 728         if (wdd)
 729                 err = watchdog_ping(wdd);
 730         mutex_unlock(&wd_data->lock);
 731
 732         if (err < 0)
 733                 return err;
 734
 735         return len;
 736 }
 737
 738 /*
 739  * watchdog_ioctl - handle the different ioctl's for the watchdog device
 740  * @file:       File handle to the device
 741  * @cmd:        Watchdog command
 742  * @arg:        Argument pointer
 743  *
 744  * The watchdog API defines a common set of functions for all watchdogs
 745  * according to their available features.
 746  *
 747  * Return: 0 if successful, error otherwise.
 748  */
 749
 750 static long watchdog_ioctl(struct file *file, unsigned int cmd,
 751                                                         unsigned long arg)
 752 {
 753         struct watchdog_core_data *wd_data = file->private_data;
 754         void __user *argp = (void __user *)arg;
 755         struct watchdog_device *wdd;
 756         int __user *p = argp;
 757         unsigned int val;
 758         int err;
 759
 760         mutex_lock(&wd_data->lock);
 761
 762         wdd = wd_data->wdd;
 763         if (!wdd) {
 764                 err = -ENODEV;
 765                 goto out_ioctl;
 766         }
 767
 768         err = watchdog_ioctl_op(wdd, cmd, arg);
 769         if (err != -ENOIOCTLCMD)
 770                 goto out_ioctl;
 771
 772         switch (cmd) {
 773         case WDIOC_GETSUPPORT:
 774                 err = copy_to_user(argp, wdd->info,
 775                         sizeof(struct watchdog_info)) ? -EFAULT : 0;
 776                 break;
 777         case WDIOC_GETSTATUS:
 778                 val = watchdog_get_status(wdd);
 779                 err = put_user(val, p);
 780                 break;
 781         case WDIOC_GETBOOTSTATUS:
 782                 err = put_user(wdd->bootstatus, p);
 783                 break;
 784         case WDIOC_SETOPTIONS:
 785                 if (get_user(val, p)) {
 786                         err = -EFAULT;
 787                         break;
 788                 }
 789                 if (val & WDIOS_DISABLECARD) {
 790                         err = watchdog_stop(wdd);
 791                         if (err < 0)
 792                                 break;
 793                 }
 794                 if (val & WDIOS_ENABLECARD)
 795                         err = watchdog_start(wdd);
 796                 break;
 797         case WDIOC_KEEPALIVE:
 798                 if (!(wdd->info->options & WDIOF_KEEPALIVEPING)) {
 799                         err = -EOPNOTSUPP;
 800                         break;
 801                 }
 802                 err = watchdog_ping(wdd);
 803                 break;
 804         case WDIOC_SETTIMEOUT:
 805                 if (get_user(val, p)) {
 806                         err = -EFAULT;
 807                         break;
 808                 }
 809                 err = watchdog_set_timeout(wdd, val);
 810                 if (err < 0)
 811                         break;
 812                 /* If the watchdog is active then we send a keepalive ping
 813                  * to make sure that the watchdog keep's running (and if
 814                  * possible that it takes the new timeout) */
 815                 err = watchdog_ping(wdd);
 816                 if (err < 0)
 817                         break;
 818                 fallthrough;
 819         case WDIOC_GETTIMEOUT:
 820                 /* timeout == 0 means that we don't know the timeout */
 821                 if (wdd->timeout == 0) {
 822                         err = -EOPNOTSUPP;
 823                         break;
 824                 }
 825                 err = put_user(wdd->timeout, p);
 826                 break;
 827         case WDIOC_GETTIMELEFT:
 828                 err = watchdog_get_timeleft(wdd, &val);
 829                 if (err < 0)
 830                         break;
 831                 err = put_user(val, p);
 832                 break;
 833         case WDIOC_SETPRETIMEOUT:
 834                 if (get_user(val, p)) {
 835                         err = -EFAULT;
 836                         break;
 837                 }
 838                 err = watchdog_set_pretimeout(wdd, val);
 839                 break;
 840         case WDIOC_GETPRETIMEOUT:
 841                 err = put_user(wdd->pretimeout, p);
 842                 break;
 843         default:
 844                 err = -ENOTTY;
 845                 break;
 846         }
 847
 848 out_ioctl:
 849         mutex_unlock(&wd_data->lock);
 850         return err;
 851 }
 852
 853 /*
 854  * watchdog_open - open the /dev/watchdog* devices
 855  * @inode:      Inode of device
 856  * @file:       File handle to device
 857  *
 858  * When the /dev/watchdog* device gets opened, we start the watchdog.
 859  * Watch out: the /dev/watchdog device is single open, so we make sure
 860  * it can only be opened once.
 861  *
 862  * Return: 0 if successful, error otherwise.
 863  */
 864 static int watchdog_open(struct inode *inode, struct file *file)
 865 {
 866         struct watchdog_core_data *wd_data;
 867         struct watchdog_device *wdd;
 868         bool hw_running;
 869         int err;
 870
 871         /* Get the corresponding watchdog device */
 872         if (imajor(inode) == MISC_MAJOR)
 873                 wd_data = old_wd_data;
 874         else
 875                 wd_data = container_of(inode->i_cdev, struct watchdog_core_data,
 876                                        cdev);
 877
 878         /* the watchdog is single open! */
 879         if (test_and_set_bit(_WDOG_DEV_OPEN, &wd_data->status))
 880                 return -EBUSY;
 881
 882         wdd = wd_data->wdd;
 883
 884         /*
 885          * If the /dev/watchdog device is open, we don't want the module
 886          * to be unloaded.
 887          */
 888         hw_running = watchdog_hw_running(wdd);
 889         if (!hw_running && !try_module_get(wdd->ops->owner)) {
 890                 err = -EBUSY;
 891                 goto out_clear;
 892         }
 893
 894         err = watchdog_start(wdd);
 895         if (err < 0)
 896                 goto out_mod;
 897
 898         file->private_data = wd_data;
 899
 900         if (!hw_running)
 901                 get_device(&wd_data->dev);
 902
 903         /*
 904          * open_timeout only applies for the first open from
 905          * userspace. Set open_deadline to infinity so that the kernel
 906          * will take care of an always-running hardware watchdog in
 907          * case the device gets magic-closed or WDIOS_DISABLECARD is
 908          * applied.
 909          */
 910         wd_data->open_deadline = KTIME_MAX;
 911
 912         /* dev/watchdog is a virtual (and thus non-seekable) filesystem */
 913         return stream_open(inode, file);
 914
 915 out_mod:
 916         module_put(wd_data->wdd->ops->owner);
 917 out_clear:
 918         clear_bit(_WDOG_DEV_OPEN, &wd_data->status);
 919         return err;
 920 }
 921
 922 static void watchdog_core_data_release(struct device *dev)
 923 {
 924         struct watchdog_core_data *wd_data;
 925
 926         wd_data = container_of(dev, struct watchdog_core_data, dev);
 927
 928         kfree(wd_data);
 929 }
 930
 931 /*
 932  * watchdog_release - release the watchdog device
 933  * @inode:      Inode of device
 934  * @file:       File handle to device
 935  *
 936  * This is the code for when /dev/watchdog gets closed. We will only
 937  * stop the watchdog when we have received the magic char (and nowayout
 938  * was not set), else the watchdog will keep running.
 939  *
 940  * Always returns 0.
 941  */
 942 static int watchdog_release(struct inode *inode, struct file *file)
 943 {
 944         struct watchdog_core_data *wd_data = file->private_data;
 945         struct watchdog_device *wdd;
 946         int err = -EBUSY;
 947         bool running;
 948
 949         mutex_lock(&wd_data->lock);
 950
 951         wdd = wd_data->wdd;
 952         if (!wdd)
 953                 goto done;
 954
 955         /*
 956          * We only stop the watchdog if we received the magic character
 957          * or if WDIOF_MAGICCLOSE is not set. If nowayout was set then
 958          * watchdog_stop will fail.
 959          */
 960         if (!watchdog_active(wdd))
 961                 err = 0;
 962         else if (test_and_clear_bit(_WDOG_ALLOW_RELEASE, &wd_data->status) ||
 963                  !(wdd->info->options & WDIOF_MAGICCLOSE))
 964                 err = watchdog_stop(wdd);
 965
 966         /* If the watchdog was not stopped, send a keepalive ping */
 967         if (err < 0) {
 968                 pr_crit("watchdog%d: watchdog did not stop!\n", wdd->id);
 969                 watchdog_ping(wdd);
 970         }
 971
 972         watchdog_update_worker(wdd);
 973
 974         /* make sure that /dev/watchdog can be re-opened */
 975         clear_bit(_WDOG_DEV_OPEN, &wd_data->status);
 976
 977 done:
 978         running = wdd && watchdog_hw_running(wdd);
 979         mutex_unlock(&wd_data->lock);
 980         /*
 981          * Allow the owner module to be unloaded again unless the watchdog
 982          * is still running. If the watchdog is still running, it can not
 983          * be stopped, and its driver must not be unloaded.
 984          */
 985         if (!running) {
 986                 module_put(wd_data->cdev.owner);
 987                 put_device(&wd_data->dev);
 988         }
 989         return 0;
 990 }
 991
 992 static const struct file_operations watchdog_fops = {
 993         .owner          = THIS_MODULE,
 994         .write          = watchdog_write,
 995         .unlocked_ioctl = watchdog_ioctl,
 996         .compat_ioctl   = compat_ptr_ioctl,
 997         .open           = watchdog_open,
 998         .release        = watchdog_release,
 999 };
1000
1001 static struct miscdevice watchdog_miscdev = {
1002         .minor          = WATCHDOG_MINOR,
1003         .name           = "watchdog",
1004         .fops           = &watchdog_fops,
1005 };
1006
1007 static struct class watchdog_class = {
1008         .name =         "watchdog",
1009         .dev_groups =   wdt_groups,
1010 };
1011
1012 /*
1013  * watchdog_cdev_register - register watchdog character device
1014  * @wdd: Watchdog device
1015  *
1016  * Register a watchdog character device including handling the legacy
1017  * /dev/watchdog node. /dev/watchdog is actually a miscdevice and
1018  * thus we set it up like that.
1019  *
1020  * Return: 0 if successful, error otherwise.
1021  */
1022 static int watchdog_cdev_register(struct watchdog_device *wdd)
1023 {
1024         struct watchdog_core_data *wd_data;
1025         int err;
1026
1027         wd_data = kzalloc(sizeof(struct watchdog_core_data), GFP_KERNEL);
1028         if (!wd_data)
1029                 return -ENOMEM;
1030         mutex_init(&wd_data->lock);
1031
1032         wd_data->wdd = wdd;
1033         wdd->wd_data = wd_data;
1034
1035         if (IS_ERR_OR_NULL(watchdog_kworker)) {
1036                 kfree(wd_data);
1037                 return -ENODEV;
1038         }
1039
1040         device_initialize(&wd_data->dev);
1041         wd_data->dev.devt = MKDEV(MAJOR(watchdog_devt), wdd->id);
1042         wd_data->dev.class = &watchdog_class;
1043         wd_data->dev.parent = wdd->parent;
1044         wd_data->dev.groups = wdd->groups;
1045         wd_data->dev.release = watchdog_core_data_release;
1046         dev_set_drvdata(&wd_data->dev, wdd);
1047         err = dev_set_name(&wd_data->dev, "watchdog%d", wdd->id);
1048         if (err) {
1049                 put_device(&wd_data->dev);
1050                 return err;
1051         }
1052
1053         kthread_init_work(&wd_data->work, watchdog_ping_work);
1054         hrtimer_init(&wd_data->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
1055         wd_data->timer.function = watchdog_timer_expired;
1056         watchdog_hrtimer_pretimeout_init(wdd);
1057
1058         if (wdd->id == 0) {
1059                 old_wd_data = wd_data;
1060                 watchdog_miscdev.parent = wdd->parent;
1061                 err = misc_register(&watchdog_miscdev);
1062                 if (err != 0) {
1063                         pr_err("%s: cannot register miscdev on minor=%d (err=%d).\n",
1064                                 wdd->info->identity, WATCHDOG_MINOR, err);
1065                         if (err == -EBUSY)
1066                                 pr_err("%s: a legacy watchdog module is probably present.\n",
1067                                         wdd->info->identity);
1068                         old_wd_data = NULL;
1069                         put_device(&wd_data->dev);
1070                         return err;
1071                 }
1072         }
1073
1074         /* Fill in the data structures */
1075         cdev_init(&wd_data->cdev, &watchdog_fops);
1076         wd_data->cdev.owner = wdd->ops->owner;
1077
1078         /* Add the device */
1079         err = cdev_device_add(&wd_data->cdev, &wd_data->dev);
1080         if (err) {
1081                 pr_err("watchdog%d unable to add device %d:%d\n",
1082                         wdd->id,  MAJOR(watchdog_devt), wdd->id);
1083                 if (wdd->id == 0) {
1084                         misc_deregister(&watchdog_miscdev);
1085                         old_wd_data = NULL;
1086                 }
1087                 put_device(&wd_data->dev);
1088                 return err;
1089         }
1090
1091         /* Record time of most recent heartbeat as 'just before now'. */
1092         wd_data->last_hw_keepalive = ktime_sub(ktime_get(), 1);
1093         watchdog_set_open_deadline(wd_data);
1094
1095         /*
1096          * If the watchdog is running, prevent its driver from being unloaded,
1097          * and schedule an immediate ping.
1098          */
1099         if (watchdog_hw_running(wdd)) {
1100                 __module_get(wdd->ops->owner);
1101                 get_device(&wd_data->dev);
1102                 if (handle_boot_enabled)
1103                         hrtimer_start(&wd_data->timer, 0,
1104                                       HRTIMER_MODE_REL_HARD);
1105                 else
1106                         pr_info("watchdog%d running and kernel based pre-userspace handler disabled\n",
1107                                 wdd->id);
1108         }
1109
1110         return 0;
1111 }
1112
1113 /*
1114  * watchdog_cdev_unregister - unregister watchdog character device
1115  * @wdd: Watchdog device
1116  *
1117  * Unregister watchdog character device and if needed the legacy
1118  * /dev/watchdog device.
1119  */
1120 static void watchdog_cdev_unregister(struct watchdog_device *wdd)
1121 {
1122         struct watchdog_core_data *wd_data = wdd->wd_data;
1123
1124         cdev_device_del(&wd_data->cdev, &wd_data->dev);
1125         if (wdd->id == 0) {
1126                 misc_deregister(&watchdog_miscdev);
1127                 old_wd_data = NULL;
1128         }
1129
1130         if (watchdog_active(wdd) &&
1131             test_bit(WDOG_STOP_ON_UNREGISTER, &wdd->status)) {
1132                 watchdog_stop(wdd);
1133         }
1134
1135         watchdog_hrtimer_pretimeout_stop(wdd);
1136
1137         mutex_lock(&wd_data->lock);
1138         wd_data->wdd = NULL;
1139         wdd->wd_data = NULL;
1140         mutex_unlock(&wd_data->lock);
1141
1142         hrtimer_cancel(&wd_data->timer);
1143         kthread_cancel_work_sync(&wd_data->work);
1144
1145         put_device(&wd_data->dev);
1146 }
1147
1148 /**
1149  * watchdog_dev_register - register a watchdog device
1150  * @wdd: Watchdog device
1151  *
1152  * Register a watchdog device including handling the legacy
1153  * /dev/watchdog node. /dev/watchdog is actually a miscdevice and
1154  * thus we set it up like that.
1155  *
1156  * Return: 0 if successful, error otherwise.
1157  */
1158 int watchdog_dev_register(struct watchdog_device *wdd)
1159 {
1160         int ret;
1161
1162         ret = watchdog_cdev_register(wdd);
1163         if (ret)
1164                 return ret;
1165
1166         ret = watchdog_register_pretimeout(wdd);
1167         if (ret)
1168                 watchdog_cdev_unregister(wdd);
1169
1170         return ret;
1171 }
1172
1173 /**
1174  * watchdog_dev_unregister - unregister a watchdog device
1175  * @wdd: watchdog device
1176  *
1177  * Unregister watchdog device and if needed the legacy
1178  * /dev/watchdog device.
1179  */
1180 void watchdog_dev_unregister(struct watchdog_device *wdd)
1181 {
1182         watchdog_unregister_pretimeout(wdd);
1183         watchdog_cdev_unregister(wdd);
1184 }
1185
1186 /**
1187  * watchdog_set_last_hw_keepalive - set last HW keepalive time for watchdog
1188  * @wdd:                Watchdog device
1189  * @last_ping_ms:       Time since last HW heartbeat
1190  *
1191  * Adjusts the last known HW keepalive time for a watchdog timer.
1192  * This is needed if the watchdog is already running when the probe
1193  * function is called, and it can't be pinged immediately. This
1194  * function must be called immediately after watchdog registration,
1195  * and min_hw_heartbeat_ms must be set for this to be useful.
1196  *
1197  * Return: 0 if successful, error otherwise.
1198  */
1199 int watchdog_set_last_hw_keepalive(struct watchdog_device *wdd,
1200                                    unsigned int last_ping_ms)
1201 {
1202         struct watchdog_core_data *wd_data;
1203         ktime_t now;
1204
1205         if (!wdd)
1206                 return -EINVAL;
1207
1208         wd_data = wdd->wd_data;
1209
1210         now = ktime_get();
1211
1212         wd_data->last_hw_keepalive = ktime_sub(now, ms_to_ktime(last_ping_ms));
1213
1214         if (watchdog_hw_running(wdd) && handle_boot_enabled)
1215                 return __watchdog_ping(wdd);
1216
1217         return 0;
1218 }
1219 EXPORT_SYMBOL_GPL(watchdog_set_last_hw_keepalive);
1220
1221 /**
1222  * watchdog_dev_init - init dev part of watchdog core
1223  *
1224  * Allocate a range of chardev nodes to use for watchdog devices.
1225  *
1226  * Return: 0 if successful, error otherwise.
1227  */
1228 int __init watchdog_dev_init(void)
1229 {
1230         int err;
1231
1232         watchdog_kworker = kthread_create_worker(0, "watchdogd");
1233         if (IS_ERR(watchdog_kworker)) {
1234                 pr_err("Failed to create watchdog kworker\n");
1235                 return PTR_ERR(watchdog_kworker);
1236         }
1237         sched_set_fifo(watchdog_kworker->task);
1238
1239         err = class_register(&watchdog_class);
1240         if (err < 0) {
1241                 pr_err("couldn't register class\n");
1242                 goto err_register;
1243         }
1244
1245         err = alloc_chrdev_region(&watchdog_devt, 0, MAX_DOGS, "watchdog");
1246         if (err < 0) {
1247                 pr_err("watchdog: unable to allocate char dev region\n");
1248                 goto err_alloc;
1249         }
1250
1251         return 0;
1252
1253 err_alloc:
1254         class_unregister(&watchdog_class);
1255 err_register:
1256         kthread_destroy_worker(watchdog_kworker);
1257         return err;
1258 }
1259
1260 /**
1261  * watchdog_dev_exit - exit dev part of watchdog core
1262  *
1263  * Release the range of chardev nodes used for watchdog devices.
1264  */
1265 void __exit watchdog_dev_exit(void)
1266 {
1267         unregister_chrdev_region(watchdog_devt, MAX_DOGS);
1268         class_unregister(&watchdog_class);
1269         kthread_destroy_worker(watchdog_kworker);
1270 }
1271
1272 int watchdog_dev_suspend(struct watchdog_device *wdd)
1273 {
1274         struct watchdog_core_data *wd_data = wdd->wd_data;
1275         int ret = 0;
1276
1277         if (!wdd->wd_data)
1278                 return -ENODEV;
1279
1280         /* ping for the last time before suspend */
1281         mutex_lock(&wd_data->lock);
1282         if (watchdog_worker_should_ping(wd_data))
1283                 ret = __watchdog_ping(wd_data->wdd);
1284         mutex_unlock(&wd_data->lock);
1285
1286         if (ret)
1287                 return ret;
1288
1289         /*
1290          * make sure that watchdog worker will not kick in when the wdog is
1291          * suspended
1292          */
1293         hrtimer_cancel(&wd_data->timer);
1294         kthread_cancel_work_sync(&wd_data->work);
1295
1296         return 0;
1297 }
1298
1299 int watchdog_dev_resume(struct watchdog_device *wdd)
1300 {
1301         struct watchdog_core_data *wd_data = wdd->wd_data;
1302         int ret = 0;
1303
1304         if (!wdd->wd_data)
1305                 return -ENODEV;
1306
1307         /*
1308          * __watchdog_ping will also retrigger hrtimer and therefore restore the
1309          * ping worker if needed.
1310          */
1311         mutex_lock(&wd_data->lock);
1312         if (watchdog_worker_should_ping(wd_data))
1313                 ret = __watchdog_ping(wd_data->wdd);
1314         mutex_unlock(&wd_data->lock);
1315
1316         return ret;
1317 }
1318
1319 module_param(handle_boot_enabled, bool, 0444);
1320 MODULE_PARM_DESC(handle_boot_enabled,
1321         "Watchdog core auto-updates boot enabled watchdogs before userspace takes over (default="
1322         __MODULE_STRING(IS_ENABLED(CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED)) ")");
1323
1324 module_param(open_timeout, uint, 0644);
1325 MODULE_PARM_DESC(open_timeout,
1326         "Maximum time (in seconds, 0 means infinity) for userspace to take over a running watchdog (default="
1327         __MODULE_STRING(CONFIG_WATCHDOG_OPEN_TIMEOUT) ")");